The present invention relates to sampling oscilloscopes, and more particularly to an equivalent time sampler for a sampling oscilloscope that uses an oscillator to develop a sample and hold trigger.
Sampling oscilloscopes are used to provide high bandwidth, voltage versus time displays of waveforms. In such a sampling oscilloscope a sample and hold circuit is triggered at several different points during the waveform. This triggering is done in an ordered fashion so that all points of the waveform are eventually sampled, as shown in FIG. 2. One common method places each successive sample point an interval deltat further from a trigger point than the last. The effect is that the sampled point, measured in degrees of the waveform period, moves monotonically and in equal increments. This is known as sequential sampling.
In a classical sequential sampler, such as shown in FIG. 1, a direct trigger is derived from the input waveform via a trigger generator. The direct trigger gates a variable delay generator to produce a delayed trigger, the amount of delay being a function of a delay control signal from a staircase generator. The delay control signal also provides a "time coordinate" for the sample. The delay trigger briefly turns on the sample and hold circuit, capturing the amplitude of the waveform. The amplitude value and time coordinate are then stored and/or displayed on a display device.
What is desired is a simplified sequential sampler that allows the observation of jitter in a waveform having a repetitive component without using an external clock.